It seemed to be a moment of truth inside the White House. Officials there protested that they had no intention of cutting money from the Black Lung Disability Trust Fund which would reduce payments to those miners suffering from the disabling consequences of inhaling coal dust while underground. They asserted that Congress liberalized the law in 1977 and 1979 without providing adequate compensation.

The program is scheduled to expend about $824 million this year, but revenues from the tax imposed on coal to pay for the fund will amount to around $275 million. Theoretically the government must meet the difference of $549 million. As in scores of similar cases, the new Reagan administration says that is too much; the government's books must be made to balance. Deficits cause inflation which Mr. Reagan is determined to end.

Sam Church Jr., president of the United Mine Workers of America, and other officials insisted at outdoor rallies here that they also want the federal budget balanced. But they charged that the government and coal operators are trying to put the burden of the particular problem on the coal miners.

Some 177,000 miners around the country are emphasizing their protest by a two-day walkout. This comes at a critical moment in the national contract negotiations by the union for its three-year agreement. Lacking a contract there could be a strike starting March 27.

Democrats in Congress nominally support the Reagan objective of reducing US deficits but complain of the speed and technicalities in the administration push. Senate Democratic leader Robert C. Byrd from the coal state of West Virginia addressed the miners before the march.

The Reagan retrenchment program was announced Feb. 18 in "A Program or Economic Recovery." The President would raise defense expenditures, cut other domestic costs, and slash personal income taxes across the board by 10 percent a year in the three-year Kemp- Roth proposal.

The big budget cuts were hastily put together by Budget Director David A. Stockman after the election and include a massive retreat by the government from the nation's health care industry. Opponents watch the miner's protest as an indication of the contest ahead and administration reaction.

Health cuts include federal contributions to medicaid, the health program for the poor and subsidies to health maintenance organizations and hospitals operated by the Public Health Service. Activities have been criticized before, but the attacks have been resisted or ignored and federalization has gone on.

Now the Reagan conservative agenda is being pressed. New Secretary of Health and Human Resources Richard S. Schweiker said Feb. 21, "This is our last opportunity and our best opportunity. If we don't do it now, we never will."

Robert M. McGlotten, lobbyist for the AFL-CIO declared, "Each one of these proposed changes has some effect on every member's district." Now comes the first potential test of strength with the miners.

UMW president Church said here that there are 4,000 deaths annually from black lung. He agreed that the insolvent miners' disability trust fund should be put "on a sound financial footing" but at the expense of the coal operators, not of the victims. The administration seeks to tighten eligibility requirements.

One difficulty for fund administrators, the labor leader charged, is that they must borrow at the high prevailing interest rate. Under one figure, 174, 400 coal miners are now receiving some form of black lung benefits.

President Reagan wants benefits to come from the industry not the taxpayer. But his generalized language does not make plain whether he would retreat from the liberalized benefit standards imposed in 1977 and 1979. He wants federal contributions curtailed immediately and ended by 1981. He asks for a "reasonable" increase in the coal tax and restrictions limiting benefits to "those that are truly medically disabled." He did not offer details and the miners did not wait either but mounted their sharp protest.